Vehicle wheels with foam filled tires are especially useful in applications involving industrial and off-the-road vehicles, where it is essential to maintain the vehicles in service, since time lost for repairs is very costly. It is known to fill tires with a curable and foamable elastomeric material, which, after heat curing, expands to a closed cell foam rubber composition that provides an operating pressure within the tire. Such foam filled tires are substantially deflation proof and almost indestructible from normal hazards, for example, bolts, nails, large holes, jagged curbs, sharp rocks, deep water, etc. Thus, foam filled tires substantially reduce the time such vehicles are down for repairs.
Examples of filled tires are shown and described in U.S. Pat. Nos. 3,022,810, 3,381,735, 3,650,865, 3,872,201, 4,060,578 and 6,623,580. U.S. Pat. No. 3,650,865 provides one example of filling a tire cavity with a curable and foamable elastomeric material to pressurize the tire. U.S. Pat. Nos. 3,650,865 and 6,623,580 describe methods of making a foam filled tire by inserting layers of a curable and foamable elastomeric material within a cured tire. The tire is then heated to cure the curable and foamable elastomeric material contained therein. The heat curing process can be performed either before, or after, the tire is mounted on a wheel rim. Heating causes the layers of the curable and foamable elastomeric material to expand and form a closed cell foam rubber composition that provides an internal tire pressure.
Tires filled with such a curable and foamable elastomeric material have a damping similar to that of a pneumatic tire and thus, provide a pneumatic-like ride, which is especially important with unsprung off-the-road vehicles. Further, the performance of such foam filled tires is often superior to the performance of tires filled with other materials. To achieve greater market acceptance, it is desirable that tire dealers be able to manufacture foam filled tires with an elastomeric material. However, many tire dealers do not have heat curing equipment. Further, the cost of such equipment and the time and energy required for the heat curing process add substantial costs to a foam filled tire made with an elastomeric material.
To avoid such costs, tire dealers often make vehicle wheels using alternative materials, for example, polyurethane. With such a process, after mounting a cured tire on a wheel rim, the tire is often prestretched for about 24 hours. Materials forming a polyurethane or a similar polymer are then injected into a tire cavity through a check valve in the wheel rim that is located in a lower-most six o'clock position. Air is vented from the tire cavity through a bleed or vent hole extending through the tread at an upper-most twelve o'clock position. The injected materials react to form a polyurethane that fills the cavity inside the tire.
A polyurethane filled wheel has several disadvantages compared to a wheel filled with a cured and foamed elastomeric material. First, the polyurethane fill provides little or no dampening and thus, gives a harsher ride, which increases vehicle wear and tear, as well as operator fatigue. Further, the polyurethane is a very hard fill material that provides a smaller tire footprint. Thus, the polyurethane filled tire has a greater ground pressure that may breakup the ground surface. In addition, the smaller footprint provides less tire traction.
Therefore, there is a need for an improved foam filled tire and method of manufacture that reduces the cost of making a tire filled with a closed cell foam rubber composition.